In the past 15 years, the use of impact assessment as an analytical tool has gradually influenced national and international discussions on trade agreements. Two main approaches predominate: sustainability impact assessments (SIA), which analyze economic, social and environmental consequences of the trade agreement, and environmental assessments, which identify the environmental effects of the trade accord. The paper analyses the EU SIA approach and the environmental approach practiced by the North American Free Trade Agreement (NAFTA). The study shows that neither the SIA nor the EA currently have the power to bring a trade accord with failing assessment grades into political peril.